Experts found those exposed to high levels of air pollution were more likely to have poor quality sperm.
The research suggests moving to the countryside could boost their chance of conceiving.
There is growing evidence linking tiny particles of traffic fumes, known as particulate matter, to a wide range of health dangers.
Researchers looked at the sperm quality of nearly 6,500 men in Taiwan. They also assessed smog levels near each participant’s home address. Those with the highest exposure to fine sooty particles – known as PM2.5 – were most likely to have abnormally-shaped sperm.
And increasing levels of pollution also resulted in a significant drop in healthy sperm.
One theory is that the heavy metals in dirty air damage DNA and alter sperm production. Scientists from the Chinese University of Hong Kong claim the changes could spell infertility for “significant number of couples.”
The study, published in the journal Occupational & Environmental Medicine, concluded: “This is an important public health challenge.”
“Given the ubiquity of exposure to air pollution, a small effect size of PM2.5 on sperm normal morphology may result in a significant number of couples with infertility,” the researchers say.
Air pollution has also been strongly linked to heart and lung deaths.
Professor Allan Pacey, Professor of Andrology at Sheffield University, said: “The main result of the paper appears to be that as the concentration of fine particulates increases, then so does the proportion of sperm which are abnormally shaped.
“Air pollution probably does have the potential to negatively influence male reproductive health. But the jury is still out about quite how and to what extent this impacts on male fertility.”
And Professor Kevin McConway, Emeritus Professor of Applied Statistics at The Open University, said: “This is an interesting study, but it’s important to be aware of its limitations.
“If I were young enough to worry about my fertility, I wouldn’t put moving to an area with cleaner air at the top of my list of actions – though there are certainly many other health-related reasons to live in cleaner air.”